At present, notebook computers using touch screens or pad computers with keyboard docking stations and the like are becoming more and more popular. Typically, when a notebook computer with a touch screen rotates its touch screen by 180° or “back flips” its touch screen to the back of the notebook computer to make the notebook computer used as a pad computer, the keyboard of the notebook computer will usually be locked. In this case, the password can only be input through the virtual keyboard displayed on the touch screen (such as the power-on password or screen lock password). However, the user experience of the virtual keyboard is usually poor. Moreover, in the case that the notebook computer or pad computer determines whether the user can use the notebook computer or pad computer by using the face recognition technology, if the user is using the notebook computer or pad computer in a dark environment, it is difficult to obtain the user's face portrait and determine whether the user can use the notebook computer or pad computer through the face recognition technology.